A. An overlay of micrographs of sequential stages of a dividing D. discoideum cell expressing GFP-dynacortin . Stationary rings are apparent. The cartoon highlights the shape of the cell cortex during the sequential shape changes. Bar, 5 μm. B. The pole-to-pole distance increases as the cleavage furrow radius decreases. As soon as the emerging daughter cells become distinguishable, their cross-sectional diameters remain constant until the completion of division. C. The vectors that were calculated to relate the contractile force to the cortical stiffness. The radius of the furrow is also the radius of curvature of the ingressing furrow cortex and γ is the minimal required contractile force if the cortical stiffness is Sc. D. The minimal estimated force required at any point of division is plotted as a function of cell shape.